1. Technical Field
The present invention relates to a method and apparatus for inspecting building service lateral connection lines in sewer systems. More particularly, the present invention relates to a method and apparatus for detecting and locating leakage-causing defects in building service lateral sewer lines.
2. Discussion of the Prior Art
Most localities have long been plagued by massive amounts of non-sewage water that taxes the capacities of water treatment facilities, which capacities might otherwise be more than sufficient to handle the actual sewage generated by the area population. Inflow (i.e., water entering the system from roof leaders, storm drains and other sources as a result of rainfall) and infiltration (i.e., the ground water entering the system through defects in pipes, joints, service connections, and manholes) account for as much as 35% of the water transported to treatment plants. The cost of transportation and treatment of this extraneous flow can run into the millions of dollars per year.
It has been found that most of the infiltration in sewer collection systems results from leaks in building service lateral sewer pipes. Conventionally, identification and repair of leaks in service laterals requires excavation and/or access to the buildings serviced by the laterals. This approach is costly as well as disruptive of activities in and around the building. An improved method and apparatus for sealing leaks in building service lateral sewer pipes is described and illustrated in U.S. Pat. No. 4,484,602 (Guthrie). Also described in that patent is a technique for detecting leaks in a service lateral whereby: the main sewer pipe is sealed at opposite sides of the lateral entrance; an inflatable elongated tube is extended into the lateral pipe to create a seal against the inner surface of the lateral remote from the entrance but creating an annular space between the tube and the lateral pipe intermediate the entrance and the seal; pressurized gas is delivered to the annular space; and a pressure transducer monitors the pressure in the annular space to determine whether or not a leak is present in the pipe. This leak detection approach has limitations in that it cannot pinpoint the location of a detected leak, and the pressure transducer is often not sufficiently sensitive to detect very small pressure changes caused by very small leaks.